International Telecommunication Union (ITU) proposes very high requirement to the next generation mobile communication system that international mobile telecommunications-advanced (IMT-Advanced), such as the maximum system bandwidth need to reach 100 MHz, peak data rate of uplink and downlink data transmission respectively need to reach 1 Gbps and 500 Mbps; at the same time, it proposes very high requirement to average spectral efficiency of system, especially to edge spectral efficiency. To satisfy the requirement of IMT-Advanced system, 3rd Generation Partnership Project (3GPP) propose using multi-points coordinated transmission technology to improve capability of system in its next generation mobile cellular communication system that long term evolution advanced (LTE-Advanced).
Multi-points coordinated transmission technology is the cooperation between multiple transmission points which are separated from each other geometrically. Generally speaking, the multiple transmission points are base stations of different cells or base stations within the same cell. Multi-points coordinated transmission technology comprises downlink coordinated transmission and uplink joint reception. Downlink multi-points coordinated transmission technology comprises two types: joint transmission and coordinated scheduling/beamforming.
Therein, in joint transmission solution, all cells in cooperative cell set send same or different data in same radio resource block to user equipment, that is to say multiple cooperative cells send data to the same user equipment at the same time. By joint transmission, the interference signals between different cells in long term evolution (LTE) system become useful signals, thereby the interference between cells is reduced. FIG. 1 shows a diagram that two cells implement joint transmission by cooperation. In the figure, the two cells send effective data to user equipment (UE) at the same time, the signals sent by the two cells merge in the air and received by the UE. That reduces the interference between cells, improves quality of the transmission signal, thereby, improves the average spectral efficiency and the cell edge transmission rate.
In coordinated scheduling/beamforming (CS/CBF) solution, only serving cell of UE sends data to the UE, at this point it is the same as transmission mode of the existing LTE standard. Other cells in cooperative cell set could use same radio resource block to serve different UE. But in LTE standard, each cell sends signal without considering interference to transmission signal of other cells, cells don't implement coordination to transmitting direction and resource between each other. However, in CBF solution, when each cell in cooperative cell set sends signal, it need to implement coordination, according to interference to signal of other cell, to reduce interference to UE in other cells as far as possible. According to the coordination of sending signal beam direction between cooperative cells, it effectively prevents the beam with strong interference, then reduces mutual interference, improves quality of receiving signal. FIG. 2 shows a diagram that two cooperative cells prevent interference sending signal beam direction of service UE, according to coordination scheduling.
But, in the existing CBF solution, each cooperative cell need to send scheduling information of sub-bands in each sub-frame to neighboring cells through X2 interface, the overhead of X2 interface is very large, it proposes higher requirement to delay and capacity of the X2 interface, then affects the application of the CBF solution in actual system.